1. Field of the Invention
The present invention relates to a novel amorphous inorganic ceramic material that exhibits excellent heat resistance and the like, and a method of producing such a material, as well as an inorganic fiber and an inorganic nonwoven fabric comprising the ceramic material, and methods of producing the fiber and fabric. Moreover, the present invention also relates to a composite material that comprises the inorganic fiber or inorganic nonwoven fabric as a reinforcing material.
2. Description of the Prior Art
Conventionally, glass fiber and carbon fiber are the most widely known reinforcing materials for composite materials. In particular, carbon fiber reinforced plastic (CFRP) exhibits superior levels of strength and elastic modulus to steel or glass fiber reinforced plastic (GFRP), and also offers superior mechanical properties.
However, in recent years, as a result of the demands to reduce the consumption of crude oil due to factors such as global warming caused by carbon dioxide and the sharp rise in the cost of crude oil, reductions in the weight of all manner of components is becoming necessary. If the quantity of CFRP or the like is reduced in order to meet these demands for weight reduction, then the strength of the resulting product tends to be unsatisfactory. In this manner, these reinforcing materials are unable to satisfy all the required properties.
Composite materials of carbon fiber and a light metal such as aluminum have been investigated as potential improvements to the situation described above, but the wetting properties of carbon fiber and a light metal are poor, and the light metal and carbon may undergo reaction at high temperatures, causing a deterioration in the strength.
On the other hand, the silicon-based fiber developed by Yajima et al. in 1975 exhibits favorable wetting with light metals, good heat resistance, and does not suffer from the problem of reaction between the light metal and the fiber at high temperatures causing a deterioration in the strength. Furthermore, methods in which a polycrystalline silicon carbide fiber is produced from an organopolysiloxane are also being investigated. However, a high temperature treatment of at least 1,600° C. is required to produce these types of fibers, and moreover, because these fibers contain phenyl groups, the Si/C elemental ratio is low, and the carbon loss ratio during heat treatment is high, meaning they face problems in terms of conserving resources, and from an economic perspective.
In recent years, methods have been proposed for preparing ultra fine silicon-based fibers by conducting fiber spinning of polymer blends. In these methods, two raw materials are used, namely a polycarbosilane that functions as a silicon precursor to the silicon-based fiber, and a resin that disappears by thermal decomposition as a matrix. Specifically, the silicon precursor is dispersed and mixed within the resin that disappears upon thermal decomposition, melt spinning is then conducted, and a heat treatment is then conducted. In the methods that use these raw materials, large quantities of hydrogen are generated during the production process, meaning safety can be problematic (patent references 1 and 2).
A method has also been proposed in which carbon fiber is reacted with silicon monoxide gas to generate silicon carbide fibers, and the resulting fibers are then subjected to heat treatment. This method requires a gaseous phase reaction to be conducted under conditions of reduced pressure and high temperature, meaning a simpler method would be more desirable (patent reference 3).
Exhaust gases discharged from vehicles and industrial machinery and the like cause atmospheric pollution, and are attracting considerable attention. Particularly in the case of diesel engine vehicles, the removal of NOx and suspended particulate matter comprised mainly of carbon is a significant issue.
Against this type of background, a large variety of different exhaust gas purification devices have been proposed. A typical exhaust gas purification device for a diesel engine is a structure in which a casing is provided partway along the exhaust pipe connected to the engine exhaust manifold, and a filter having very fine apertures formed therein is then disposed within this casing, but the material for this filter suffers from cracking caused by temperature fluctuations and dissolution loss (patent reference 4). In order to overcome these problems, exhaust gas purification devices that use either a metallic nonwoven fabric (patent reference 5) or a silicon carbide-based nonwoven fabric (patent reference 6) as the filter have also been proposed. However, because these materials are short fibers, the material strength tends to be low, and the methods are also extremely expensive due to raw material synthesis problems that require the synthesis of a polysilane from dimethyldichlorosilane, followed by the synthesis of a polycarbosilane or polytitanocarbosilane.
[Patent Reference 1] EP 0435065 A1
[Patent Reference 2] JP 2004-360115 A
[Patent Reference 3] JP 7-18520 A
[Patent Reference 4] JP 6-92753 A
[Patent Reference 5] U.S. Pat. No. 5,908,480
[Patent Reference 6] JP 2004-60096 A